The present invention concerns signal analysis and pertains particularly to defining a channel mask for the purpose of monitoring wavelength division multiplexing (WDM) transmission systems.
Wavelength division multiplexing (WDM) fiber optic transmission systems use between 4 and 500 laser signals to transmit information. Each laser signal resides within a specific frequency channel. The channel is defined by its center frequency and signal power. It is desirable to monitor the performance of each laser signal within the many channels of a WDM system.
In prior art multi-wavelength meter (MWM) systems the performance of the laser signals within the channels is listed in a tabular (textual) format. The task of monitoring the channels is left to the user and his ability to analyze the data using an external computer to assess the performance of the individual laser signals relative to the channel center frequency, minimum and maximum power and frequency constraints. This method is complicated because it requires the user to develop additional software and to use additional hardware to make the measurement.
In accordance with the preferred embodiment of the present invention, multiple signals are monitored, for example, by an instrument used for monitoring wavelength division multiplexing (WDM) transmission systems. For each monitored frequency channel, an active mask is initialized. The active mask includes an operating window defined by a minimum frequency, a maximum frequency, a minimum amplitude and a maximum amplitude. Each signal is monitored to determine when the signal strays outside the operating window. An alarm is generated when the signal strays outside the operating window or outside the active mask boundaries.
In the preferred embodiment, the active mask for each monitored frequency channel additionally includes a center frequency, a minimum channel frequency limit, a maximum channel frequency limit and a power threshold limit.
In the preferred embodiment, when an alarm is generated an alarm entry is made. Each alarm entry indicates channel information such as average frequency, minimum frequency, maximum frequency, minimum power, maximum power, current power, current frequency. Each alarm entry also indicates time of alarm generation, date of the alarm generation and an error code indicating a region of operation at the time of the alarm generation.
A user has flexibility in selecting mask parameters. For example, the minimum frequency, the maximum frequency, the minimum amplitude and the maximum amplitude can vary between all active masks. Alternatively, active masks within specified frequency bands can have identical channel spacing with varying minimum amplitudes. Alternatively, active masks within specified frequency bands can have identical channel spacing with identical minimum/maximum amplitudes and frequencies.
The present invention simplifies the process of monitoring multiple laser signals by user created masks or automatically created masks. The instrument used the mask to verify that each laser signal is within the prescribed frequency and power range. The invention also accounts for the fact that in WDM systems the noise power floor is wavelength dependent, i.e., accounts for the fact that each laser is set to a unique power level resulting in a uniform optical-signal-to-noise ratio for all laser lines/channels.